Panel mounting apparatus



y 1961 J. BELL ET AL 2,993,290

PANEL MOUNTING APPARATUS Filed Feb. 15, 1960 5 Sheets-Sheet 1 F 4541 F a r "a Ill/III/II/A,

INVENTORS. JEROME 554A 77904 A KELLY ATTORNEYS I 3 Sheets-Sheet 2 Filed Feb. 15, 1960 INVENTORS. JEROME BELL fl77-/0L A AZZL) A/PRY A. F/TES July 25, 1961 Filed Feb. 15, 1960 J. BELL ET AL 2,993,290

PANEL MOUNTING APPARATUS 3 Sheets-Sheet 3 INVENTORS. JEROME BELL ATf/OL A. KELLY L/4A AY L. F7755 sired shape.

United States Fatent G 2,93,290 PANEL MOUNTING APPARATUS Jerome Bell, Kalamazoo, Mich, Larry L. Fites, Perry Township, Miami County, Ind., and Athol A. Kelley, Schoolcraft Township, Kalamazoo County, Mich assignors to The Upjohn Company, Kalamazoo, M1ch., a corporation of Delaware Filed Feb. 15, 1960, Ser. No. 8,660 6 Claims. (Cl. 40-152) This invention relates to an apparatus and is more particularly concerned with a device for detachably mounting a sheet of material.

The invention consists in a device for detachably mounting a sheet of material which comprises in combination a supporting member having a longitudinal undercut groove and a sheet, adapted to be supported in said groove, having means engaging the undercut edges of said groove said means being disposed along the edge of said sheet and being temporarily collapsible to a position such that the edge of said sheet can be inserted into said groove when said means is collapsed.

The means, which is attached to the sheet and which engages the undercut edges of the groove in the supporting member, takes the form of a collapsible wedgeshape member which is disposed along the edge of the sheet.

The wedge-shape member is constructed, as will be del scribed hereinafter, so that it can be collapsed temporarily, by manual pressure, and can be inserted, in the collapsed state, into the groove of the supporting member. After insertion into the groove the collapsed member tends to assume its former wedge shape and thereby engages the undercut edges of said groove. Further, the wedge-shape member is so constructed that it will maintain said sheet in firm engagement with said supporting member and yet can be removed therefrom, when required, without diificultyv Thus the present invention provides a simple and elegant device for mounting a sheet of material whereby the sheet can be readily mounted in a supporting member and removed readily thereupon without the use of sep arate locking devices and without the need for detaching part or parts of the supporting member before inserting or removing the sheet.

The device of the present invention can take various forms according to the particular use to which it is to be put. Thus the present invention can be used to suspend a sheet of material by a small portion of, or substantially the whole portion of, one edge thereof. The sheet of material can be of any desired shape and the edge thereof which isused for attachment to the supporting member can be straight or curved. Alternatively, the present invention can be used to suspend or mount a sheet of material by engagement with a supporting member at more than one point along its edge. Thus the invention can be used in supporting a sheet of material in a frame or like supporting member which conforms to the contours of tee edge of said material. Here again the sheet and the supporting member can be of any do- The supporting member of the device of the invention can be provided with means known in the art for suspending said member from a wall or ceiling or for enabling said supporting member to stand freely.

The devices of the present invention are particularly useful in connection with the display or printed matter, such as advertising matter, public notices, calendars, and the like. It is to be understood, however, that the present invention is of general applicability and is not to be constructed as limited to any particular use.

In the accompanying drawings:

FIGURE 1 is a plan view of a sheet member according ice to the invention showing one embodiment of the means for attaching the sheet to the supporting member.

FIGURE 2 is a cross-sectional view of the sheet member shown in FIGURE 1 after the latter has been folded.

FIGURE 3 is a cross-sectional view of one embodiment of the supporting member according to the invention.

FIGURE 4 is a cross-sectional view of another embodiment of the supporting member according to the invention.

FIGURE 5 is a cross-sectional view of yet another embodiment of the supporting member according to the invention.

FIGURE 6 is a cross-sectional view showing the sheet member of FIGURES 1 and 2 after mounting in the supporting member shown in cross-section in FIGURE 3.

FIGURE 7 is a cross-sectional view of another embodiment of the supporting member according to the invention.

FIGURE 8 is a plan view of a sheet member according to the invention showing another embodiment of the means for attaching the sheet to the supporting member.

FIGURE 9 is a plan view of a sheet member according to the invention showing another embodiment of the means for attaching the sheet to the supporting member.

FIGURE 10 is a plan view of a sheet member according to the invention showing another embodiment of the means for attaching the sheet to the supporting member.

FIGURE 11 is a cross-sectional view of the sheet member shown in FIGURE 10 after the latter has been folded.

FIGURE 12 is a cross-sectional view showing the sheet member of FIGURE 10 after mounting in the supporting member shown in cross-section in FIGURE 4.

FIGURE 13 is a perspective View of a sheet member according to the invention showing another embodiment of the means for attaching the sheet to the supporting member.

FIGURE 14 is a cross-sectional view showing the sheet .member of FIGURE 13 after mounting in the supporting member shown in cross-section in FIGURE 4.

FIGURE 15 is a perspective view of a sheet member according to the invention showing another embodiment of the means for attaching the sheet to the supporting member.

FIGURE 16 is a cross-sectional view of the sheet member shown in FIGURE 15.

FIGURE 17 is a cross-sectional view showing the sheet member of FIGURE 15 after mounting in the supporting member shown in cross-section in FIGURE 4.

FIGURE 18 is a perspective drawing with a cutaway section showing a rectangular sheet mounted in a rectangular frame according to one embodiment of the in vention.

The present invention-will be described firstly in its application to the attachment of a sheet of material to a supporting member along a part or the whole of one edge of the sheet. This particular mode of mounting a sheet of material in a supporting member is illustrated by reference to FIGURES 1 to 3. In FIGURE 1 the sheet of material 1 is provided along a straight edge 2 with a flap F represented by the area bounded by the edges 3, 3 and 4 of the flap and that portion of edge 2 which is common to the sheet 1 and the flap. It is to be noted that the flap F can extend over the whole length of the edge 2 of the sheet 1 or can occupy only a part thereof as shown in FIGURE 1. The sheet 1 and the flap F can be cut from a single sheet of material or the flap F and the sheet 1 can be constructed separately and joined together along the common edge 2 by means known in the art, for example by providing the flap F, along its edge which is common with the edge 2 of the sheet 1, with an extension which extension is attached adhesively to the sheet 1. The flap F is constructed of flexible, resilient material which can be scored and folded Without cracking or tearing. Suitable such material includes paper, which paper can, if desired, be stiffened or coated on one or both surfaces, cardboard, flexible plastic sheeting such as polyethylene, polystyrene, and the like. The sheet 1 can be constructed of the same material as the flap F and indeed, as previously mentioned, the flap can be integral with the sheet. Alternatively the flap F can be constructed separately from materials such as those described above and attached to the sheet 1 in which case the sheet 1 need not be flexible and can be constructed from materials. such as wood, metal, and

non-flexible plastic materials.

'the line which runs parallel to said edge 2 and is spaced therefrom by a variable distance 6. The flap F is then bent by folding along the length of each of the score lines 2 and 5 so that the inside angle at each of the folds is approximately 90 degrees. FIGURE 2 shows a crosssectional view of the flap and sheet after folding theflap along the score lines 2 and 5.

The supporting member of the device according to the invention, as illustrated at A, comprises a strip of material having a longitudinal undercut groove. Said supporting member can be fabricated from a variety of materials ineluding metal, wood, plastic and the like. Preferably said supporting member is constructed from extrudable materials such as aluminum, polystyrene and the like since the fabrication of said supporting member is thereby greatly simplified. The essential requirement of the supporting member is that the groove therein be undercut, i.e., the entrance to said groove is narrower than the floor thereof. The exterior contours of the supporting member are non-functional and can be modified to suit aesthetic and other considerations. The inner contours of the groove of the supporting member can also vary and typical examples are shown incross-section in FIGURES .3, 4, and 5. In the cross-sectional view of the supporting member shown in FIGURE 3 the sidewalls slope inwardly and upwardly from the floor of the groove so that the width of the entrance 11 to the groove is less than the width of the floor 10. .Generally speaking, it has been found that best results are obtained when the width of the entrance 11 is approximately one-half of the width of the floor 10. The edges 12 and 13 of the entrance to the groove are preferably rounded to facilitate the insertion of the sheet in the manner described below. The dimensions of said groove bear the following relationship to the dimensions of the various portions of the sheet 1 of FIGURE 1. The distance 6 between the score lines 2 and 5 on the flap F should preferably be intermediate between the width of the entrance 11 and that of the floor 10 of the groove shown in cross-section in FIGURE 3. The width 7 of the portion of the flap F which lies between the score line 5 and the edge 4 in the sheet 1 of FIGURE 1 is advantageously of the same order of magnitude as the depth 14 of the groove of FIGURE 3.

The method of mounting the sheet of FIGURE 1 in the supporting member shown in cross-section in FIG- URE 3 is as follows. The flap F, after folding into the position shown in cross-section in FIGURE 2, is collapsed about the fold along the score line 2 by manual pressure along the score line 5 so that the flap is brought into contact with the main part of the sheet I. The edge thereby formed along the score line 2 is inserted into the groove via the entrance 11 until the edge of the sheet makes contact with the floor of the groove. After insertion of the sheet into the groove in this manner, the flap on the sheet tends to assume its original contours, i.e., those shown in cross-section in FIGURE 2. Thus, as illustrated in FIG- URE 6, that portion of the flap F which liesbetween the score lines 2 and 5 is aligned parallel to and in contact with the floor 10 of the groove, while the inner edges of the entrance to the groove are engaged by the surfaces of the main portion of the sheet and of the portion of the flap which lies between the score line 5 and edge 4 of the flap.

When the flap edge of the sheet 1 and the supporting member are brought into engagement as described the sheet is held firmly in place. However, the sheet can be removed readily from the supporting member, when required, by pulling the sheet in a direction vertical to the floor of the groove whereby the flap is collapsed about the score line 5.

The cross-sectional design of the groove in the supporting member can be modifiedin a number of ways provided that the relative widths of the entrance to the groove and the floor thereof are not modified. Thus, as previously mentioned, the contours of the outer surface 8 of the supporting member can be modified in any desired fashion for purposes of decoration, etc. and do not effect the mode of operation of the device. The surface 9 of the inner walls of the groove can also be modified, for example, said surface can be made convex or con cave provided that the dimensions of the entrance and the floor of the groove are not affected thereby. The walls of the groove can also be made substantially vertical with respect to the floor of the groove as shown in FIGURE 4. In that case it is necessary to provide the inner surfaces of the entrance to the groove with lips which protrude inwardly thereby maintaining the relationship between the dimensions of the entrance to the groove and the floor of the groove. The shape of these lips can be varied but preferably the surfaces of said lips slope inwardly and downwardly towards the floor of said groove. 7 The exterior walls of the groove shown in crosssection in FIGURE 4 can be modified or decorated as desired.

In FIGURE 5 there is shown a cross-sectional view of a further modification of the supporting member of the invention. In this modification one wall of the groove is substantially vertical with respect to the floor of the groove whereas the other wall of the groove slopes inwardly and upwardly from the floor of the groove. The same relationship, discussed in connection with the groove shown in cross-section in FIGURE 3, between the width of the entrance to the groove and the width of the floor of the groove applies in the present instance. Also, the contours of the exterior walls of this further modification can be varied without affecting the mode of operation of the groove.

In a further modification of the construction of the ,groove of the supporting member, a groove having .a

cross-sectional view intermediate between those shown in FIGURES 3 and 5 can be employed. Thus a groove can be constructed in which each wall of the groove slopes inwardly and upwardly from the floor of the groove but one wall is inclined to the vertical at a greater angle than the other. Such a groove is shown in cross-section in FIGURE 7. r

Other modifications of the construction of the undercut groove of the supporting member, which can be made without affecting the operation of the supporting member in accordance with the present invention, will be obvious to one skilled in the art.

The mode of construction of the flap F and the sheet 1 illustrated in FIGURE 1 can also be subjected to modification without departing from the scope of the present invention. Thus, the shape and size of the remainder of sheet 1 can be varied without affecting the mode of attachment of the sheet and the supporting member. Two of the remaining edges of the sheet 1 other than the edge 2 have been shown as straight and parallel-to each other in FIGURE 1 but said edges and the fourth edge (not shown) can be of any desired shape.

' Further, the edge 2 of the sheet 1 shown in FIGURE 1 need not be straight but can be curved in which case the score line is also curved so that it runs paralleltothe score line 2. Where the edge of the sheetfbearing the flap is curved it is necessary to'provide V-shap'ed indentations in the flap F in order that said flap can be folded without buckling or distortion, The construction of a flap attached to the curved edge of a sheet is illustrated in FIGURE 8, wherein the score lines 16 and 17 run parallel to each other and are spaced apart by a distance determined by the considerationsmentioned' previously. The V-shaped indentations 15 are constructed so that the points thereof are coincident with the inner score line 16. It will be appreciated that the angle at the apex of the indentations must be greater'than a minimum which is a function of the radius of curvature ,ofthe edge of the sheet. The most suitable dimensions of the indentations and the most suitable distance between said indentations will vary as the radius of curvature of the edge of the sheet is varied and can be' determined readily in any particular instance by experimentation.

[When the edge of the sheet, to be mounted in a su porting member according 'to the present invention, is

curved it is, of course, necessary that the supporting member be curved in a corresponding manner. The method of inserting the flap-bearing curved edge of the sheet into the appropriately curved supporting member corresponds exactly to that adopted when the flap-bearing edge is' straight.

In a further modification of the invention the fl'ap attached to the sheet carries parallel score lines the inner most of which is not integral with the edge of the'sheet in FIGURE 9 wherein the lines 18 and 19 represent the score lines. This mode of construction is particularly advantageous where the flap does not extend along the whole length of the edge of the sheet to which it is attached. Thus, by constructing the flap so that the distance 22 between the innermost score line 19 and the line of the edge 21 of the sheet is substantially equal to the depth of the groove in the supporting member, the main portion of the sheet will, after insertion of the folded flap in the supporting member, lie wholly outside the groove of the supporting member. The distance 23 between the outermost score line 18 and the edge of the flap is preferably equal to the depth of the groove in the supporting member so that the edge 20 does not protrude from the supporting member after the insertion of the flap into the supporting member. The above type of construction can also be modified as shown in FIGURE 8 for use with a sheet having a curved edge.

In a further modification of the invention the sheet is provided with a flap constructed in the manner illus mately midway between said lines. The relative distances between the score lines 26 and 27, between the score line 27 and the edge 24 of the flap, and between the score line 26 and the edge 25 are governed by the same considerations discussed above for the arrangements shown in FIG- URES 1, 8 and 9. The construction shown in FIGURE 10 when folded has the configuration shown in crosssection in FIGURE 11. After folding in this manner the flap is pinched so that it collapses about the score line 28 and the folds along the score lines 26 and 27 are brought together to form a single edge which is then inserted in the groove of the supporting member. After insertion into the supporting member in this manner the flap assumes the configuration shown in FIGURE l2. Said flap is held firmly within said supporting member but .pevertheless can be withdrawn readily by pulling the main so but is spaced therefrom. Such construction is illustrated portion of the sheet in a direction vertical to the floor of the groove.

v In yet a further modification of the invention the sheet is provided with a vflap constructed in the manner illustrated in FIGURE 13. In this construction the sheet is provided along a portion of its edge 29 with a plurality of flaps disposed on opposite sides of the sheet. In'the actual construction shown the flaps are disposed alternately on one side or the other of the sheet but the exact disposition of the flaps can'be varied as desired. Each flap is folded along the edge 29 common to the flap and the main portion of the'sheet and is also folded through an angle of approximately degrees about a score line 30. The distance between the score line 30 and the edge '29 of the sheet should be the same for all the flaps on the same side of the sheet but the flaps on one side can differ from those on the 'other side in respect of this dimension. The total distance between the score lines 30 in the flaps on opposite sides of the sheet should be intermediate be- "tween the width of the entrance of the groove and the width of the floor thereof in the supporting member. The distance between each of the score lines 30 and the corresponding edges 31 of the flaps can be varied but is preferably of ,the same order as the depth of the groove in the supporting member. The construction of FIGURE 13 has the advantage that, by employing flaps of uniform dimen sions, and inserting the flap-edge of the sheet in a groove of symmetrical cross-section, the sheet after insertion into the supporting member, is centrally disposed therein as 'shown in FIGURE 14, rather than being forced into engagement with one'of the edges of the groove in said supporting member as shown, for example, in FIGURE 6.

A modification of the sheet member shown in FIGURE 13 can be employed in which the edge 29 of the sheet is provided with two continuous flaps disposed one on each side of said sheet rather than the series of alternating flaps shown in FIGURE 13. a

A further modification of the invention is illustrated in FIGURE 15 wherein the sheet member is provided along a part of its edge 32 with two flaps 33 and 34, the edges 35 arid 37 of said flaps running parallel to-the edge 32 of the sheet. The flap 33 is preferably integral with the main portion of the sheet and, indeed, where the flap extends along the whole edge of the sheet, the edge 35 of the flap can be the edge of said sheet. The flap 34 is attached to the sheet, for example, by means of an extension (not shown) united adhesively to said sheet, along the edge 32. The flap 34 is provided with a score line 36 running parallel to the edge 32 of the sheet. The flap 34 is folded about the score line 36 so that the outer edge 37 of said flap lies in the angle formed by the flaps 33 and 34. FIGURE 16 shows a cross-sectional view of the sheet after folding in this manner. The width 38 of the flap 33 is substantially equal to the depth of the groove of the supporting member in which the sheet is to be mounted. The width 39 of that portion of the flap 34 which lies between the edge 32 and the score line 36 can be varied but is preferably equal to or slightly greater than the width 38 of the flap 33. The width '40 of the portion of flap 34 which lies between the score line 36 and the outermost edge 37' of said flap is intermediate between the width of in FIGURE 17. If desired, the flap 33 can be provided I with a raised portion at or approximating the edge 35 on 76.

the side adjacent to the flap 34 whereby the edge 37 of r 7 the flap 34 can be retained within the :two flaps.

The invention has been described so far in relation to .the mounting of a sheet of material in a supporting member by means of a collapsible wedge-shaped member disposed along a part of or the whole of one side of said sheet. In a preferred embodiment of the invention the sheet is provided with a collapsible wedge-shaped member along more than one of its edges. In particular the invention can be applied to the mounting-of a-sheet of material in a frame which completely surrounds the edge of the sheet and has the same'contours as the periphery of the sheet. The shape of the sheet which can be mounted in such fashion can be varied within wide limits. For example, a square or rectangular sheet of material can be provided along part or thewhole of two opposite sides with flaps such as those shown in any of FIGURES l, 9,, l0, l3, and 15, and. can be mounted thereby in a supporting member the inner edges of which have the same contours as the edge of said sheet and which has undercut grooves, such as those having crosssections shown in FIGURES 3, 4, 5, and 7, along the inner edges of the sides'corresponding to the flapbearing sides of the sheet. A particular example of a rectangular sheet mounted in a rectangular frame is shown in :FIGURE 18, the mode of mounting of the sheet in the groove being illustrated in the cutaway portion.

Similarly, the sheet can be elliptical or circular in shape and can be provided at two oppositely disposed portions of its edge with flaps such as those shown in FIGURE 8, or those shown in FIGURES 9 or 13 when :modified by provision of V-shaped indentations as shown in FIGURE 8. The supporting member is constructed to fit said sheet and is provided with undercut grooves along the portions of its inner edge which correspond to the flap-bearing edges of the sheet.

It is to be noted that where the sheet is completely circumscribed by the supporting member, and the pesie angle formed b9 ripheral edges of the sheet correspond exactly to the inner contours of the supporting member, as described above, it is essential that the sheet itself, in addition to the flap members, be constructed of flexible material as hereinbefore defined. Thus, where the supporting member forms a frame for the sheet, the sheet is inserted into the supporting member by collapsing one of the flap members of said sheet, in the manner previously described and inserting the collapsed flap-bearing edge into one of the grooves in the supporting member and then collapsing the second flap on said sheet and inserting the collapsed flap into the other groove on said supporting member. However, in order to insert the second flap it is necmsary to flex the sheet, otherwise the second flapbearing edge of the sheet cannot be brought into juxtaposition with the groove of the supporting member.

Where the sheet takes the form of a square or rectangle having flaps on two opposite sides thereof and is mounted in a supporting member of corresponding square or rectangular shape it is possible to mount said sheet-with its surface bowed outwardly or inwardly by making the width of the sheet between the flap-bearing edges greater than the distance between the corresponding grooves in the supporting member.

We claim:

1. A device for detachably mounting a sheet of flexible, resilient material which comprises in combination a frame and a sheet of flexible resilient material, said frame being provided with grooves at two substantially geometrically opposed places on its inner edges, the inner surfaces of the entrance to said grooves having lips, the width of the gap between said lips being less than the width of the floor of said grooves, and said flexible, resilient :sheet be ng provided with flaps at the edges thereof corresponding to the position of said grooves in said frame, each of said flaps having two folds running parallel to each'other and to the edge of said sheet, the distance between said folds being less than the minimum distance between the entrance .to, and 'the'floorof said grooves and being intermediate between the width of the floor of said g 'Ooves and the width ofthe gap between the lips at theentrance of said grooves, and the distance between the outer edge of said flaps and the fold nearest thereto being not less than the distance between the entrance to, and the floor of, said grooves.

'2. A device for detachably mounting a sheet of flexible, resilient material which comprises in combination a frame and a sheet of flexible resilient material, said frame being rectangular in shape and being provided with grooves on the inner edge of twoopposite sides thereof, the inner surfaces of the entrance to said grooves having lips, the width of the gap between said lips being less than the widthof the floor of said grooves, and said flexible, resilient sheet taking the form of a rectangle of substantially the same dimensions as the inner edges of said frame, said sheet being provided with flaps along the major portion of the sides thereof corresponding to "the grooved sides of said frame, each of said 'flaps'having two folds running parallel to .eachother and to the edge of said sheet, the distance between said folds beingless than the minimum distance between the entrance to, and the floor of said grooves and being intermediate between the width of the floor ofsaid grooves andv the width of the gap between the lips at the entrance of said grooves, and the distance between the outer edge of said flaps and the fold nearest thereto being not less than the minimum distance between the entrance to, and the floor of, said grooves.

3. A device for detachbly mounting asheet of flexible,

resilient material which comprises in combination a frame and a sheet of flexible resilient material, said frame being rectangular in shape and being provided with grooves on the inner edge of two opposite sides thereof, the inner surfaces of the entrance to said grooves having lips, thewidth of the vnarrowest point of the gap between said lips being approximately one-half of the width of theiloor of said grooves, and said flexible, resilient sheet taking the form of a rectangle of substantially the same dimensions as the inner edges of said frame, said sheet being provided with ham along the major portion of the sides thereof corresponding to the grooved sides of said frame, each of said flaps having two folds running parallel to each other and to the edge of said sheet, the distance between said folds being less than the minimum distance between the entrance to, and the floor of, said grooves and being intermediate between the width of the floor of said grooves and the width of the gap between the lips at the entrance of said grooves, and the distance between the outer edges of said .flaps and the fold nearest thereto being not less than the minimum distance between thelips and the floor of said grooves. V

4. A device for detachably mounting a sheet of flexible, resilient material which comprises in combination a frame .and a sheet of flexible resilient material, said frame being rectangular in shape and being provided with grooves on the inner edges of two opposite sides thereof, the inner surfaces of the entrance to said grooves having lips whose surfaces slope inwardly and downwardly towards the floor of said grooves, the width of the narrowest point of the gap between said lips being approximately one-half of the width of the floor of said grooves, and said flexible, resilient sheet taking the form of a rectangle of substantially the same dimensions as the inner edges of said frame, said sheet being provided with flaps along the major portion of the sides thereof corresponding to the grooved sides of said frame, each of said flaps having two folds running parallel to each other and to the edge of said sheet, the distance between said folds being less than the minimum distance between the entrance to, and the floor of, said grooves and being intermediate between the width of the floor of said grooves and the width of the gap between the lips at the entrance of said grooves, and the distance between the outer edges of said flaps and the fold nearest thereto being not less than the minimum distance between the lips and the floor of said grooves.

5. A device for detachably mounting a sheet of flexible, resilient material which comprises in combination a frame and a sheet of flexible, resilient material, said frame being rectangular in shape and being provided with grooves on the inner edges of two opposite sides thereof, the inner surfaces of the entrance to said grooves having lips whose surfaces slope inwardly and downwardly towards the floor of said grooves, the width of the narrowest point of the gap between said lips being approximately one-half of the width of the floor of said grooves, and said flexible, resilient sheet taking the form of a rectangle of substantially the same dimensions as the inner edges of said frame, said sheet being provided with flaps along the major portion of the sides thereof corresponding to the grooved sides of said frame, each of said flaps having two folds running parallel to each other and to the edge of said sheet, the distance between said folds being less than the minimum distance between the entrance to, and the floor of, said grooves and being intermediate between the width of the floor of said grooves and the width of the gap between the lips at the entrance of said grooves, and the distance between the innermost fold of said flaps and the inner edge of said flaps being substantially the same as the distance between the outermost fold and the outermost edge of said flaps and corresponding substantially to the depth of the grooves in said frame.

6. A device as claimed in claim 5 wherein each of the flaps on the edges of the flexible resilient sheet lies on the same side of said sheet after folding.

References Cited in the file of this patent UNITED STATES PATENTS 2,749,636 Viglietta June 12, 1956 

